Electrophoretic printing



Aug. 18, 1964 e. OSTER 3,145,156

ELECTROPHORETIC PRINTING Filed Nov. 15, 1961 2 Sheets-Sheet l FIG. I

:rlB

1 FIG. 3 f" FIG. 4 I

FIG. 5

INVENTOR. GERALD OSTER ATTORNEYS United States Patent 3,145,156 ELECTROPHORETIC PRINTING Gerald Oster, New York, N.Y., assignor to The Carters This invention relates in'general to printing and related processes such as image transfer, erasure, and retrieval, and particularly to methods employing electrophoresis to cause a visible, or otherwise detectable, material composed of particles charged with respect to their surrounding medium to be transferred from one place to another. The basic methods of this invention may be used in a variety of ways, such as to print characters from a stylus, from formed electrodes corresponding to-the characters, or'from insulating stencils having selectively conductive regions; for the erasureof characters already printed; for the identification of counterfeit copies through the retrieval of maskedirnages or materials; for multi-color printing from a single plate; for simultaneous printing of several images and generally for any use wherein intelligence represented by a detectable material is applied to or removed from a conductive sheet or other medium in which the particles are mobile.

The processes of this invention center generally about the known fact that relatively charged particles, in a mobile state, may be caused to move in an electrical field, and that some particles move faster than others in a direction which depends on the sign of the relative charge. The relative charge may result from the particles themselves being charged, e.g. ions or charged colloids, or from the presence of a charged medium surrounding neutral particles. Thus, if a source sheet wet with a liquid containing mobile charged particles is put next to a Wet recipient sheet, and electrodes of opposite potential are placed in contact with the outside faces of the sheets,

the particles will be transferred from the source to the recipient sheet. If one electrode is formed as a character, the material transferred will represent that character.

The material to be transferred may itself be colored, 4

and therefore suitable for printing to form a visibly distinct image. Many dyestuffs, for instance, exist in solution as charged particles or ions susceptible to electrophoresis. In addition materials which exist in solution or dispersion as charged particles, although colorless in themselves, will react chemically to produce a colored, or otherwise visibly detectable product, and other materials are known which, although colorelss, may be rendered visible by subsequent treatments, such as exposure to heat or ultra-violet radiation.

In the processes of this invention, relatively charged particles of detectable material in a medium in which they are mobile are caused to be transferred by an electrical field in patterns corresponding to characters or other forms of intelligence representation. The rate of transfer depends on the potential gradient, and may be quite rapid if high voltages are employed. The current required, on the other hand, is only that exceedingly small amount represented by the net charge transferred, and the energy requirements are accordingly far lower than encountered in prior art processes in which printing or the like isaccomplished by electrical effects. Those previously devised utilizing the application of a voltage for printing have depended also on ancillary less efficient reactions which require large amounts of energy, as for heating the material to cause a change of state, or for electrolysis or other electrolytic processes which require energy to alter the charge of the material transferred. In the processes of this reaction such ancillary reactions are avoided.

3,145,156 Patented Aug. 18,1964

Mobility of the particles, which is required for transfer by electrophoresis in the processes of this invention, is easily provided by providing a fluid medium in the source sheet contiguous with a fluid mixture in the recipient sheet. Generally the source sheet will contain a solution or dispersion of an ionic dye or other detectable relatively charged material, and the recipient sheets will contain a solvent or other dispersing liquid in which the particles are mobile. In both the source and recipient sheets, the liquid should preferably exist as a continuous phase extending through the sheet within a solid matrix retaining the liquid.

Printing according to this invention may make use of a source sheet, which is wet with an aqueous solution of an ionic dyestuii and an adjacent recipient sheet which is wet with water or with a dilute electrolyticsolution. The application of a voltage between two electrodes which contact the sheets, with the electrode in contact with the outer face of the recipient sheet having a charge opposite that of the dye ion, will produce aprinted character on the recipient sheet. The electrode may be formed as a character, or it may be a plate with which is used a stencil of insulating material having a selectively conductive or cut out area forming the character.

A character formed of an ionic dye, as by the method described in the previous paragraph, or by conventional printing methods, maybe erased, or reduced in its intensity, by the same general technique, except with the potential reversed so as to cause the dye to be remove to an adjacent sheet.

' In more versatile systems making use of the methods of this invention, several sheets may be assembled in a stack and printed upon selectively, as the distance through which the charged particles may be moved by electrophoresis depends on the magnitude and duration of the applied potential, and may thus be' controlled. If several recipient sheets are wet with waterand stacked on a source sheet impregnated with an aqueous solution of an ionic dye, the application of a voltage of relatively low level (short duration or low magnitude or both) will cause the dye to be moved only to the sheet adjacent to the source sheet, whereas the application of a voltage of larger level will result in printing upon a sheet more remote from the source sheet. Depending on the amount of dye within the source sheet, printing may or may not remain on the intermediate sheet through which the dye has migrated. In some cases all of the dye may migrate completely through the intermediate sheet with none remaining;- in other cases fresh amounts of dye'from the source sheet will be retained in the intermediate sheet. I I a In many cases advantageous use maybe made ofa source sheet containing several different types of charged materials having difierent specific rates of migration; one type may be utilized to print on one sheet in a stack of recipient sheets, while another type is simultaneously printed upon a diiIerent, sheet of the stack. Where different types dyes have different signs of charge, one may be utilized for printing on a recipient sheet on one side of the source sheet and the other for printing simultaneously on a recipient sheet on the other side of the source sheet.

A further feature of which use may be made in systems for carrying out the methods of this inventionarises from the negative image formed on the source sheet as a positive image is formed on an adjacent sheet. When the source sheet contains only a singlecharged material, two copies of the image may be made with each character impression, a positive one and a negative, one. By providing two marking materials of different mobilities in the source sheet, three images may be formed with each character impression, two positive images on two differ- TABLE I Specific Relative Mobilities of Various Dyestuffs "In alcohol Specific mohi y, No Mfr. deslg. Mir. C.I. No. Charge o1ns.Xl0-

secJvolt/ cm.

1 Pontacyl Light Yel- DnP0nt. 1008 A 6.7

low Crude Ground. 2... Pontacyl Red Rubinc do 14720 A 5, 67

R Crude Ground. 3... Pontacyl Carmine 6B do 18055 A 5, 04

Extra Cone. 4... Pontacyl Green N.V. .do 44025 A 4.. 41

Extra. 5... Iontacyl Green BL .-..do 42085 A 5. 67

Extra Cone. 6-.. Pontacyl RR Brildo 42735 A 6. 3

liant Blue. 7... lontacyl Violet RC... .-...do A 504 a 8.-. Poxngacyl Fast Violet .-..do 45100 A 6. 3 9... Pontacyl Violet 41317.. do 42576 A 5. 67 10.. Pontacyl Fast Violet 7 do 42571 A 4. -11

10B Conc. 11-, Pontacyl Violet do 4.2650 A 5. 0 1

C4BN. 12 1 %13t:acy11 1 ...--d0 20-170 A 3.15 U a 13 Crocein Scarlet N ..do 27290 A 4. 41 l4 Pontamine l ast Tur- --.-(l0 7 1180 A 3. 78

quoise SG-LD cone. 160%. 1 Pontamine Black ---..do A 2, 52

. E Double. 1 Capracyl Yellow N .(10 A 1.89 17 Cgrgiagcyl Yellow .--..d0 1081 A 2. 52 1g Capracyl Orange R ...-.do 1079 A 4 3 Crude Ground! 7 19 Capracyl Red B .....(10 1160 A 1.57

Crude Ground?" 20 Luxol Fast Red A g 2 TLA451.* 21 Luxol Fast Bed L* A c5 22 Luxol Fast Red A 5, 4

TLA387.* 23 Paper Yellow L A 9. 46 24 Anramine Base.. 0 3. 78 25 Auramine Com: 0 4, 41 I 2 Metanil Yellow... A 3 15 27 Ptxltachrome Falvme A 3. 78 Orange 11 A 3.15 A S. 19 A 1. 89 A 8.09 A 0. 3

C 1. 89 C 1. 26 C 1. 26 36 Brilliant Green C 2.83

ta s. 37 Victoria Small Green 7 (3 4. 08

Crystals. 3g Sevron Blue 76 C 2. 83 39 Soluble Blue R C 0. 90 40 Methylene Blue 2X..- C 1. 89 41 Anthraquinone Violet. A 6. 3 42 Crystal Violet Extra 0 1. 26

Pure APN. 43.. Ink Violet B G 1. 26 44 Resorcin Brown 3R..- A 2. 52 45 Nigrosine WSJ A 6. 3

Crystals. 46 Nigrosine WSB Conc- A 6.3 47.. Rotalin Red S Cone... C 3, 1 4s Solantine Violet 13.... A 1. 57

49 Solantine Brown 3RL. A 2. S3 50 Wool Yellow Extra A 6. 3

Cone. 51 Wool Yellow CL A 6. 7 52 Wool Orange A A 4. 09

Cone. 53 Wool Orange FF A 3 54.. Wool Green S Cone..- A 5. 9 55.- Wool Violet 4BN A g ()9 misc).

Table l-Contmued Specific mobility, No Mir. (lesig. Mfr. 0.1. No. Charge oms. 1O-

sec/volt] cm.

56.. Chromolan Yellow N. National 19010 A 5. 04 Aniline 57.- Cigrfimolan Red G tlo 18800 A 4. 00

i 58.. Chprlomolan Green do 13425 A 3.02 59.. Orange SS 4. 41 60.. Fnehsine P Conc. 5.9

200%. 61.- Brilliant Bed GL.. 3. 78 6 Green L. Extra 200%.. 5. 3 1 53.. FastO Violet BG 00110.. 6. 93

20 64.- Iosol Red 5. 9 65.. Iosol Blue*... 8.10 66.. Fast Orange A C0nc.. 3.4 67.. Fast Blue 6G-HV 2. 29

68.. Fast Blue 6G 3. 78 69.. Auraniine 3.15 70.- Fast Light Yellow....

ZGMIL. 71.. D dz C Orange No. 4.- A 3. 78 72.. Azorubine Extra 13 A 6.3 73.. Fast Crimson GR A 8. 08

Cone. 74.. Ball Point Pen ink A 12. 9

Red Z3784.* 75.. Croceine Scarlet SS.-. A 1.10 76-- Brilliant Scarlet 3R... A 15. 75 77.- Croeeine Scarlet A 6. 3

M00 No. 90.

*In alcohol.

Various representative systems in which the methods of this invention may be used are described in greater detail below, with reference to the accompanying drawings in which:

PEG. 1 is a schematic representation in cross section of a simple arrangement of electrodes and source and recipient sheets arranged for elcctrophoretic printing in accordance with this invention; I

PEG. 2 illustrates the transfer of the character A from a source sheet to a recipient sheet, as by the system illustrated in FIG. 1, showing the formation of positive and negative images;

FIG. 3 is a schematic representation in cross section of an arrangement of electrodes with intermediate source and recipient sheets and a stencil corresponding to the character to he formed in accordance with the methods of this invention;

FIG. 4 is a schematic representation in cross section of an arrangement for printing in accordance with this invention, wherein the source sheet contains a mixture of charged materials of diiiercnt sign, with a recipient sheet on either side of the source sheet;

FIG. 5 isa schematic representation in cross section of an arrangement which features the formation of characters on selective recipient sheets from a single source sheet;

PEG. 6 is a schematic representation in cross section of an assembly for printing on several sheets in different colors, making use of the different mobilities of the dyes;

FIG. 7 is an exploded view illustrating schematically an arrangement whereby tri-colored prints may be made in a single operation from a single plate;

FIG. '8 is a schematic representation in cross section showing the mechanism for multi-colored printing illustrated in FIG. 6; and

FIG. 9 is an exploded view illustrating the process of this invention employed for image retrieval from an obscure background which masks the image until developed electrophoretically.

. The following examples describe in detail various representative printing and related processes utilizing the method of this invention, and are given as illustrative of its scope.

EXAMPLE 1 with an aqueous solution of a charged dyestuff is placed adjacent to the recipient sheet 12 which has been Wet with water, and the two are placed on a base electrode 14. vA printing electrode 16 is placed in contact with the top surface of the recipient sheet 12, and upon the application of a potential from a source, 18 between the base electrode 14 and character electrode 16 particles of charge opposite the charge of the character electrode 16 are caused to migrate from the source sheet to the recipient sheet 12. In an actual operation, the source sheet 10 was a sheet of Whatman No. 1 filter paper impregnated with an aqueous solution containing 2 percent by weight of F.D.C. Red #4 and the recipient sheet 12 was a sheet of Whatman No. 1 filter paper impregnated with a 0.1 M solution of potassium chloride. The two sheets were placed in face-to-face contact between the electrodes, as described above and were then energized from a. 100 microfarad condenser which was initially charged to a potential of 4000 volts, with the character electrode 16 being positive. I P

Upon separation of the sheets, a distinct character corresponding to the shape of the character electrode 16 was imprinted onthe recipient sheet 12 forming a positive image, and a whitened area, corresponding to a negative image of the character electrode 16 was distinctly visible in the source sheet 10, as illustrated in FIG. 2, wherein the character is depicted as the A. i

The sheets were reassembled and returned to their positions between the electrode, as illustrated in FIG. 1, and the electrodes were then energized with the opposite polarity. Upon separation of the sheets, it was observed that the character originally imprinted on the recipient sheet 12 was substantially removed.

EXAMPLE 2 The source sheet 10 and the recipientsheets 12, prepared as described with reference to FIG. 1, were placed on opposite sides of a stencil 20-having a cut-out area 21, as illustrated in FIG. 3, and these were then placed between a base electrode 14 and a coextensive top electrode 22. Uponthe application of a potential from the source 18, a character corresponding to the cut-out area of the stencil was imprinted on the recipient sheet 12, while a negative image from the depletion of coloring material was formed on the source sheet 10.

EXAMPLE 3 V Al mixture of charged coloring materials may be utilized methyl. violet B, a dye of which the color particles. are

positive,'and 2 percent of F.D.C. Red #4, a dye of which the colored particles are negative. Recipient sheets 12a and 12b prepared as described in the previous examples were placed on opposite sides of the source sheet, and the sandwich was then placed between the base electrode 14 F and the character electrode 16. The application of a negative potential of 20 volts DC. to the character electrode 16 resulted in the simultaneous formation of a blue 'in red and that in the lower recipient sheet 121) in blue.

EXAMPLE 4 Dyes of the same charge but differing mobilities may be employed to print selectively on one or more recipient sheets as illustrated in FIG. 5. and 12d, each consisting of Whatman No. 1 filter paper Two recipient sheets 12c impregnated with a 0.1 aqueous solution of potassium chloride were placed in face-to-face contact with each other and were then laid on a source sheet 10, consisting of a Whatman No. 1 filter paper impregnated with an aqueous solution containing 2 percent by weight of Brilliant Scarlet BR and 2 percent by weight of Wool Green S. The stack of papers was placed on a base electrode 14, and two character electrodes 16a and 16b were placed in contact with the top surface of the upper recipient sheet 12d. By applying a positive DC. voltage of 400 volts to electrode 16a, and simultaneously applying to the other character electrodes 1641a voltage of 200 volts, characters corresponding to, electrode 16a were imprinted on the lower recipient sheet 120, while a character corresponding to electrode 16b was imprinted on the upper recipient sheet 12d.

EXAMPLE 5 v Printing selectively on one or more of several recipient sheets can also be effected by controlling the duration and sign of a given voltage, and by utilizing dyes of different mobilities and polarities. In this example a source sheet containing four dyes, two anionic and two cationic, was used for printing on six recipient sheets, in the assembly illustrated in FIG. 6. The source sheet 10 consisted of a I Whatman No. l filter paper impregnated with an aqueous solution containing 2 percent by weight of each of: Brilliant Scarlet 3R (Cl. No. 16255, anionic), methylene blue 2X (Cl. No. 52015, cationic), Pontacyl Fast Violet C4BN (Cl. No. 42650, anionic), and Auramine (Cl. No. 41000, cationic yellow); Three recipient sheets 122, 121', 12g, 12h, 123i and 12 each consisting of Whatman No. 1 filter paper after being wet with tap water and pressed to remove the excess were stacked on each side of the source sheet 10. The array was placed on a base electrade 14 and a character electrode 16 was placed on top .of the stack under slight pressure. Two runs were made at DC. voltages of 20 volts applied for 30 seconds, first with the character electrode 16 positive and secondly with the character electrode negative. Characters were printed as follows:

Positive Negative Red/purple. Purple/blue. Purple. Turquoise. Yel w.

In this example, the cationic yellow dye and anionic red dye were of the greater mobility and printed on recipient sheets farther removed from the'source sheets than the dyes of lesser mobility. Multiple printing in difierent colors in this manner affords a convenient means of making multiplicate copies for many kinds of commercial transactions.

EXAMPLE 6 V A system for multi-colored printing from a single plate is illustrated schematically in FIGS. 7 and 8. The figure to be printed is illustrated on the lower face of a plate 30, each area there being defined by an isolated conductive area by which a characteristic potential may be applied to each separate area. For instance, it may be desired to print the hull of the sailboat illustrated in red, the sails and clouds in white, the sea and sky in blue, and the shore in green. As each color is to require a different energization characteristic, the areas corresponding to these various pictorial features must be electrically isolated. For this purpose the plates may be formed by conventional printed circuit techniques, with insulating spaces between the adjacent areas and separate electrical leads to each separate area. A source sheet 32, e.g. filter paper impregnated with an aqueous solution of dye-stuifs corresponding to the several colors to be printed is placed on a base electrode plate 34, and is covered with a recipient sheet 36 on which the print is to be made. A second recipient sheet 33 is laid over the first sheet 36 to receive and retain a dye which has been transferred through the first recipient sheet as in printing a color from a low mobility material which follows after a higher mobility dye of the same charge.

The principles of simultaneous multi-color printing, utilized in the embodiment described with reference to FIG. 7, are illustrated schematically in H6. 8. The source sheet 32 is impregnated with four different colored materials, two positively charged, and two negatively charged, one of each charge being relatively highly mobile and one being less mobile. By controlling the magnitude and duration of the charge applied at each electrode region, I

one of the four or mixtures, may be printed. Table ll shows four typical dyestuffs which are identified by reference symbols and shown schematically in FIG. 8.

In FIG. 8, the source sheet 32, and the two recipient sheets 36 and 3d, are shown between the base electrode 34 and character electrode 363. The latter is formed with four electrically isolated conductive regions Ella, Bill), 390, and 3M to which voltages of different magnitude and signs ray be applied independently. These regions may correspond for instance to the several parts of the sailboat picture shown in HS. 7, or they may be small areas arranged to form a screen for printing dots in a halftone pattern. As shown region Eda is energized at volts, 3% at v., Mic at 20 v., and Edd at -40 v.,'so that at region Ella only the more mobile negatively charged red dye is printed on the lower recipient sheet as, while at region dill), the red dye is transferred to the upper recipient sheet 31$, and the less mobile negatively charged green dye is printed on the lower recipient sheet 36. Similarly the least negatively charged region Ede prints the more mobile positively charged yellow dye (-lin recipient sheet 36, while the most negatively charged region Ilild prints the less mobile positively charged blue dye (-1-) in the recipient sheet 36.

EXAMPLE 7 A system for counterfeit detection is illustrated schematically in H6. 9, wherein an authentic ticket is imprinted with a generally black field by conventional techniques. This field serves to obscure identifying characters, illustrated in dotted lines, printed also by conventional techniques within the field by means of one or more charged dyestuffs. Identification of an authentic ticket requires the presence of proper code characters, which may be rendered visible by applying a moistened sheet of paper over the field, and passing a current between the ticket and paper in order to print sufficient of the charged dyestur'f to detect the code characters. Various alternative schemes may also be employed, for instance, the code characters may be obscured within certain printed visible characters, forming part of a serial number for other printing ordinarily appearing on the ticket, and detectable upon electrophoretic removal in accordance with a predetermined code system. in some cases, as where the ticket is to be used over and over again, and repeatedly subjected to this type of analysis, it may be desired to return the electrophoretically removed identifying material after each scrutiny, and this may be done by simply reversing the field after proper identifica tion has been made. 7

From the foregoing description it will be seen that this invention provides for printing and related operations in a novel and versatile manner having a great variety of uses. Single or multiple copies of matter to be printed may be formed as illustrated by Examples l4, in one or more colors. Matter already printed may be erased, as shown in Example 1, or developed for identification purposes as illustrated in Example 7, with or without returning the detectable material to the original print. Thus it is contemplated that the basic techniques disclosed herein may be employed for many purposes not specifically mentioned, but for which others will find them useful.

This invention has been described with reference to its presently preferred embodiments but it is expected that obvious modifications will occur to those skilled in the art and familiar with this disclosure. Such modifications may be made without departing from the scope of this invention.

Having thus disclosed my invention and described in detail preferred embodiments thereof, 1 claim and desire to secure by Letters Patent: I

1. The method of printing by the electrophoretic transfer of material, which comprises providing a source sheet having at one surface a fluid phase containing relatively charged mobile particles of a detectable material capable of electrophoretic transfer and a recipient sheet having at one surface a contiguous iluid phase in surface-to-surface contact with said one surface of said source sheet, and establishing an electrical field effective to establish electrophoretic migration across said sheets to cause said charged material to transfer from an origin within said source sheet to a destination within said recipient sheet, tie charge of said material being unaltered between said origin and said destination, said material defining a predetermined figure which is transferred to said recipient sheet and forms an image thereon independently of any electrolytic process.

2. The method of printing by the electrophoretic transfer of material, which comprises providing a source sheet having at one surface a fluid phase containing relatively charged mobile particles of a detectable material capable of electrophoretic transfer and a recipient sheet having at one surface a contiguous fluid phase in surface-to-surface contact with said one surface of said source sheet, placing electrodes at opposite sides of said sheets and establishing an electrical field effective to establish electrophoretic migration across said sheets to causesaid charged material to transfer from an origin within said source sheet to a destination within said recipient sheet, the charge of said material being unaltered between said origin and said destination, one of said electrodes defining a predetermined figure, material corresponding to which is transferred to said recipient sheet and forms an image thereon independently of any electrolytic process.

3. The method of printing by the electrophoretic transfer of-material, which comprises providing a source sheet having at one surface a fluid phase containing relatively charged mobile particles of a detectable material capable of electrophoretic transfer and a recipient sheet having at one surface a contiguous fluid phase in surface-to-surface contact with said one surface of said source sheet, establishing an electrical field effective to establish electrophoretic migration across said sheets to cause said charged material to transfer from an origin within said source sheet to a destination within said recipient sheet, thecharge of said material being unaltered between said origin and said destination, and providing selectively conductive means in said field adjacent said sheets to restrict the transfer of said material to a pro-determined figure which is transferred to said recipient sheet and forms an image thereon independently of any electrolytic process.

4. T he method of printing by the electrophoretic transfer of material, whichcomprises providing a source sheet having a fluid phase extending through said sheet and containing relatively positively charged mobile particles of a first detectable material capable of electrophoretic transfer, and also containing relatively negatively charged mobile particles of a second detectable material capable of electrophoretic transfer, and at least tworecipient sheets each having at one surface a contiguous fluid phase in surface-to-surface contact with opposite sides of said source sheet, and establishing an electrical field effective to establish electrophoretic migration across said sheets to cause said charged materials to transfer from an origin with said source sheet to destinations within said recipient sheets, the charge of said material being unaltered between said origin and said destination, said materials defining pre-dctermined figures which are transferred simultaneously to both of said recipient sheets and form an image thereon independently of any electrolytic process.

5. The method of printing which comprises providing a source sheet having at one surface a fluid phase containing relatively electrically charged mobile particles of a detectable imaterial, placing a first recipient sheet having a contiguous fluid phase extending through said first recipient sheet in face-to-face contact with said source sheet, and placing a second recipient sheet having at one surface a contiguous fluid phase in face-to-face contact with said first recipient sheet to form an array, applying an electrical field defining a figure by means of electrodes on opposite sides of said array at one location at a voltage and for a period to cause said material to transfer to one of said recipient sheets, and applying an electrical field defining a figure by means of electrodes on opposite sides of said array at a second location at a voltage and for a period tovcause said material to transfer-to the other of said recipient sheets, whereby said sheets are printed upon selectively.

6. The method of printing which comprises providing a source sheet having at one surface a fluid phase containing relatively charged mobile particles of several differently colored materials of different mobilities, placing a first recipient sheet having a contiguous fluid phase extending through said first recipient sheet in faoe-to-face contact with the surface of said source sheet, and placing a second recipient sheet having at one surface a contiguous fluid phase in face-to-face contact with the other side of said first recipient sheet, thereby forming an array, applying an electrical field in a selected first area by means of electrodes on opposite sides of said array at a voltage and 10 for a period to cause one of said colored materials to transfer to said first recipient sheet in said first area, and applying an electrical field in a selected second area by means of electrodes on opposite sides of said array at a voltage and for a period to cause another of said colored .materials to transfer to said first recipient sheet in said second area, whereby said first recipient sheet is printed upon in different colors.

7. The method of printing by the electrophoretic transfer of material from an imaged sheet having at one surface a fluid phase containing relatively charged mobile particles of a detectable material capable of electrophoretic transfer, defining a predetermined figure, comprising placing a recipient sheet having at one surface a contiguous fluid phase in surface-to-surface contact with said one surface of said imaged sheet, and establishing an electrical field effective to establish electrophoretic migration across said sheets to cause said charged material to transfer from an origin withinsaid source sheet to a destination within said recipient sheet, the charge of said material being unaltered between said origin and said destination, said material defining said pre-determined figure which is transferred to said recipient sheet and forms an image thereon independently of any electrolytic process.

8. The method defined by claim 7 wherein the electrical field .is applied at a voltage and for a duration to remove substantially all of the detectable material from the imaged sheet.

References Cited in the file of this patent UNITED STATES PATENTS 2,306,082 Prest Dec. 22, 1942 2,421,735 Prest June 3, 1947 2,567,362 Berkman et al. Sept. 11, 1951 2,888,392 Grassman et al May 26, 1959 3,010,883 Johnson et al. Nov. 28, 1961 FOREIGN PATENTS 317,444 Germany Dec. 16, 1919 609,155 Great Britain Sept. 27, 1948 OTHER REFERENCES Chemical Abstracts, volume 55, April 3, 1961, column 6217f [Konstantinov et al., Kolloid Thur., 1959, volume 21, pages 747-753]. 

1. THE METHOD OF PRINTING BY THE ELECTROPHORETIC TRANSFER OF MATERIAL, WHICH COMPRISES PROVIDING A SOURCE SHEET HAVING AT ONE SURFACE A FLUID PHASE CONTAINING RELATIVELY CHARGED MOBILE PARTICLES OF A DETECTABLE MATERIAL CAPABLE OF ELECTROPHORETIC TRANSFER AND RECIPIENT SHEET HAVING AT ONE SURFACE A CONTIGUOUS FLUID PHASE IN SURFACE-TO-SURFACE CONTACT WITH SAID ONE SURFACE OF SAID SOURCE SHEET, AND ESTABLISHING AN ELECTRICAL FIELD EFFECTIVE TO ESTABLISH ELECTROPHORETIC MIGRATION ACROSS SAID SHEETS TO CAUSE SAID CHARGED MATERIAL TO TRANSFER FROM AN ORIGIN WITHIN SAID SOURCE SHEET TO A DESTINATION WITHIN SAID RECIPIENT SHEET, THE CHARGE OF SAID MATERIAL BEING UNALTERED BETWEEN SAID ORIGIN AND SAID DESTINATION, SAID MATERIAL DEFINING A PREDETERMINED FIGURE WHICH IS TRANSFERRED TO SAID RECIPIENT SHEET AND FORMS AN IMAGE THEREON INDEPENDENTLY OF ANY ELECTROLYTIC PROCESS. 